1. Field of the Invention
The present invention relates to a technique of suppressing image deterioration caused by a foreign substance adhered to the surface of an optical low-pass filter or the like in an image sensing apparatus using an image sensor such as a CCD sensor or CMOS sensor.
2. Description of the Related Art
In a conventional lens-interchangeable digital camera, a foreign substance (to be simply referred to as dust hereinafter) such as dust or mote is sometimes adhered to an optical system or the surface of an image sensor cover glass or optical filter arranged in front of an image sensor (which will be generically referred to as an image sensor optical component). When dust is adhered to the image sensor optical component, it blocks light, and an image at the light-blocked portion is not shot, degrading the quality of the shot image.
Such dust on the image sensor is generally adhered not to the surface of the image sensor but to the surface of the cover glass or optical filter. The imaging state changes depending on the aperture value or pupil position of the imaging lens. More specifically, when the aperture value is almost the full-aperture one, the dust image blurs, and even if small dust is adhered, it does not matter. When the aperture value is large, a sharp dust image is formed, and even small dust adversely affects the entire image. To solve this problem, there is known a method of making dust less noticeable. According to this method, an image of only dust on an image sensor is prepared in advance by shooting a white wall or the like while setting the lens to a large aperture value. This image is used in combination with a shot still image (see Japanese Patent Laid-Open No. 2004-222231).
There have recently been proposed digital cameras with a moving image shooting function in addition to a still image shooting function. When a lens-interchangeable digital camera has the moving image shooting function, the aperture value and pupil position of the imaging lens change during moving image shooting in accordance with a lens operation (e.g., zoom operation). As a result, the imaging state of dust on the image sensor changes in every frame of the moving image. It is necessary to pay attention to the correspondence between an image shot for dust detection and actually shot images associated with it. If the method described in Japanese Patent Laid-Open No. 2004-222231 is simply applied to moving image shooting, the correspondence must be cumbersomely checked for each frame of the moving image.